1. Field of the Invention
The present invention relates to multilayer plastic composites, multilayer plastic pipe, and various articles comprising such multilayer plastic composites.
2. Discussion of the Background
Plastic pipes made from polyamide are known and are employed for a variety of applications. In order to achieve their objective, the pipes must be, inter alia, inert to the medium flowing in them and must be resistant to high and low temperatures and mechanical stresses.
Single-layer pipes are not always capable of satisfying the necessary requirements. In the case of transport of, for example, aliphatic or aromatic solvents, fuels or the like, they exhibit considerable disadvantages, such as a poor retention of the medium being transported, undesired changes in dimension, or inadequate resistance to mechanical stresses.
It has been attempted to overcome these disadvantages by means of multilayer pipes (DE-A 35 10 395, 37 15 251, 38 21 723, 40 01 125, and 40 01 126). However, practical implementation of these proposals has shown that, although some disadvantages can be overcome, the overall property profile is still unsatisfactory.
German Patent 38 27 092 describes a multilayer plastic pipe which contains, from the inside outwards, layers of polyamide, polyvinyl alcohol, polyamide and polyester. The polyester here is only employed in a thin outer layer in order to allow relatively high short-term heat resistance to be achieved. It is known to persons skilled in the art that by far the majority of polymers, including polyamides and polyesters, are incompatible with one another, which is why no adhesion is achieved between the laminate layers in the production of multilayer composites. However, an adhesion-based bond between the individual polymer layers is absolutely essential in industrial applications.
In particular, permeation of methanol-containing fuels has only been reduced to an inadequate extent by means of the above-mentioned proposals. Reduction in permeation by using novel intermediate layers is therefore of crucial importance, because, in particular, the legally permitted emission values are constantly being reduced.
Thus, there remains a need for a multilayer plastic composite which is a good barrier to the transported or contained medium, in particular to methanol-containing fuels, and which exhibits satisfactory dimensional stability and satisfactory resistance to mechanical stresses. In particular, there remains a need for a multilayer plastic pipe which is a good barrier to the transported medium, in particular to methanol-containing fuels, and which exhibits satisfactory dimensional stability and satisfactory resistance to mechanical stresses.